Torque control strategy for management of creep and grade hold torque in a wheeled vehicle whose powertrain includes a rotary electric machine

Abstract

A torque control strategy control for management of regenerative braking in a motor vehicle. A first processor ( 12 ) processes throttle request data ( 20 ) and torque modification data ( 40 ) from a second processor ( 14 ) to develop motor torque request data ( 28 ) for controlling rotary electric machine torque. The second processor processes brake request data ( 26 ), the throttle request data, and operating data from the at least one operating data source to develop friction brake torque data ( 30 ) for controlling friction brake torque applied to the vehicle and the torque modification data for the first processor. The two processors interact such that as long as the operating data from the at least one operating data source does not require that regenerative braking torque be limited, the torque modification data supplied to the first processor from the second processor equates to the brake torque request data, and the friction brake torque data does not cause the friction brakes to be applied, and when the operating data from the at least one operating data source calls for some limiting of the regenerative braking torque, the amount of limiting is subtracted from the torque modification data and the friction brake torque data equates to that amount of limiting for causing the friction brakes to be applied in that amount. At zero and near-zero speeds grade hold torque is calculated according to a formula and added to the friction torque.

What is claimed is:  
     
       1. A motor vehicle comprising: 
       road-engaging wheels;  
       a powerplant comprising a rotary electric machine that is operatively coupled through a drivetrain to the road-engaging wheels and that is capable both of delivering traction torque to the wheels and of imposing regenerative braking torque on the wheels;  
       friction brakes for applying friction brake torque to the wheels;  
       a throttle request source;  
       a brake request source; a  
       at least one operating data source furnishing operating data that, at certain times, calls for limitation of regenerative braking torque;  
       at least one processor for processing throttle request data from the throttle request source and torque modification data to develop motor torque request data for controlling rotary electric machine torque and for processing brake request data from the brake request source, the throttle request data, and operating data from the at least one operating data source to develop friction brake torque data for controlling friction brake torque applied to the wheels and the torque modification data;  
       wherein as long as the operating data from the at least one operating data source does not require that regenerative braking torque be limited, the torque modification data equates to the brake torque request data from the brake request source, and the friction brake torque data does not cause the friction brakes to be applied, and when the operating data from the at least one operating data source calls for some limiting of the regenerative braking torque, the amount of limiting is subtracted from the torque modification data and the friction brake torque data equates to that amount of limiting for causing the friction brakes to be applied in that amount; and  
       wherein for vehicle speeds greater than zero speed, but less than or equal to a threshold, a grade hold friction brake torque that is a function of vehicle speed is added to the friction brake torque data.  
     
     
       2. A motor vehicle as set forth in claim  1  in which the grade hold friction brake torque is determined by a formula. 
     
     
       3. A motor vehicle as set forth in claim  2  in which the formula is          T   GH     =       [     1   -                w     w   th         ]     *     T   c                       
       where T GH  is the grade hold friction brake torque, T C  is canceled rotary electric machine torque that corresponds to the torque modification, ω is vehicle speed, and ω th  is the threshold. 
     
     
       4. A motor vehicle as set forth in claim  2  in which the threshold is calibratable. 
     
     
       5. A motor vehicle as set forth in claim  2  including a applying a multiplication factor to the formula to proportionately increase or decrease the formula result in response to changing throttle and brake requests. 
     
     
       6. A motor vehicle as set forth in claim  2  in which the formula comprises the grade hold friction brake torque having an inverse functional relationship to vehicle speed. 
     
     
       7. A control for a motor vehicle that has road-engaging wheels, a powerplant that includes a rotary electric machine that is operatively coupled through a drivetrain to the road-engaging wheels and that is capable both of delivering traction torque to the wheels and of imposing regenerative braking torque on the wheels, and friction brakes for applying friction brake torque to the wheels, the control comprising: 
       a throttle request source;  
       a brake request source;  
       at least one processor for processing throttle request data from the throttle request source and torque modification data to develop motor torque request data for controlling rotary electric machine torque and for processing at least brake request data from the brake request source and the throttle request data to develop friction brake torque data for controlling friction brake torque applied to the wheels and the torque modification data;  
       wherein the torque modification data equates to the brake torque request data from the brake request source when regenerative braking torque is not being limited, and the friction brake torque data does not cause the friction brakes to be applied, and when the regenerative braking torque is being limited, the amount of limiting is subtracted from the torque modification data and the friction brake torque data equates to that amount of limiting for causing the friction brakes to be applied in that amount; and  
       wherein for vehicle speeds greater than zero speed, but less than or equal to a threshold, a grade hold friction brake torque that is a function of vehicle speed is added to the friction brake torque data.  
     
     
       8. A control as set forth in claim  7  in which the grade hold friction brake torque is determined by a formula. 
     
     
       9. A control as set forth in claim  8  in which in which the formula is          T   GH     =       [     1   -                w     w   th         ]     *     T   c                       
       where T GH  is the grade hold friction brake torque, T C  is canceled rotary electric machine torque that corresponds to the torque modification, ω is vehicle speed, and ω th  is the threshold. 
     
     
       10. A control as set forth in claim  8  in which the threshold is calibratable. 
     
     
       11. A control as set forth in claim  8  including applying a multiplication factor to the formula to proportionately increase or decrease the formula result in response to changing throttle and brake requests. 
     
     
       12. A control as set forth in claim  8  in which the formula comprises the grade hold friction brake torque having an inverse functional relationship to vehicle speed. 
     
     
       13. A method of operating a motor vehicle that has road-engaging wheels, a powerplant comprising a rotary electric machine that is operatively coupled through a drivetrain to the road-engaging wheels and that is capable both of delivering traction torque to the wheels and of imposing regenerative braking torque on the wheels, and friction brakes for applying friction brake torque to the wheels, a throttle request source, a brake request source, and at least one operating data source furnishing operating data that, at certain times, calls for limitation of regenerative braking torque, the method comprising: 
       processing throttle request data from the throttle request source and torque modification data, to develop motor torque request data for controlling rotary electric machine torque;  
       processing brake request data from the brake request source, the throttle request data, and operating data from the at least one operating data source to develop friction brake torque data for controlling friction brake torque applied to the wheels and the torque modification data;  
       wherein as long as the operating data from the at least one operating data source does not require that regenerative braking torque be limited, the torque modification data equates to the brake torque request data from the brake request source, and the friction brake torque data does not cause the friction brakes to be applied, and when the operating data from the at least one operating data source calls for some limiting of the regenerative braking torque, the amount of limiting is subtracted from the torque modification data and the friction brake torque data equates to that amount of limiting for causing the friction brakes to be applied in that amount; and  
       when vehicle speed is greater than zero speed, but less than or equal to a threshold, adding a grade hold friction brake torque that is a function of vehicle speed to the friction brake torque data.  
     
     
       14. A method as set forth in claim  13  including determining the grade hold friction brake torque according to a formula. 
     
     
       15. A method as seaport in claim  14  in which in which the formula is          T   GH     =       [     1   -                w     w   th         ]     *     T   c                       
       where T GH  is the grade hold friction brake torque, T C  is canceled rotary electric machine torque that corresponds to the torque modification, ω is vehicle speed, and ω th  is the threshold. 
     
     
       16. A method as set forth in claim  14  including calibrating the threshold. 
     
     
       17. A method as set forth in claim  14  including applying a multiplication factor to the formula to proportionately increase or decrease the formula result in response to changing throttle and brake requests. 
     
     
       18. A method as set forth in claim  14  in which the formula comprises the grade hold friction brake torque having an inverse functional relationship to vehicle speed.